Gunfire erupted at a gay nightclub in Orlando early Sunday, with multiple injuries reported.

At least 50 people were killed and more than 30 hospitalized when a gunman opened fire at a nightclub in Orlando early Sunday morning. Authorities are calling the attack on Pulse, a popular gay bar in the city's downtown, an act of domestic terrorism.

Orlando Police Chief John Mina said that the gunman, armed with an assault rifle, a handgun and a suspicious "device," began shooting inside the club at around 2 a.m., the New York Times reports. He continued shooting outside the venue, where an officer tried to confront him, then returned to the club and started shooting again while taking hostages. Police identified 29-year-old Omar Mateen as the shooter.

At around 3 a.m., the club posted an ominous note on its Facebook page: "Everyone get out of pulse and keep running."

At 5 a.m., police detonated a "controlled explosion" to clear the club and rescue the hostages, according to the Times. After a shootout with at least nine police officers, the gunman was found dead inside Pulse. Police were searching the club for possible explosives Sunday morning.

The Federal Bureau of Investigation is assisting local authorities handling the incident, the Orlando Sentinel reports. Agents said that the suspect "may have leanings toward extreme ideologies." Police said that the suspect was not from the Orlando area and was "organized and well-prepared," the Times reports.

"This is an incident, as I see it, that we certainly classify as domestic terror incident," said Orange County Sheriff Jerry Demings, according to the Washington Post.

Donald Trump and Hillary Clinton both reacted to news of the shooting. "Really bad shooting in Orlando," Trump tweeted. "Police investigating possible terrorism. Many people dead and wounded."

"Woke up to hear the devastating news from FL," Clinton wrote. "As we wait for more information, my thoughts are with those affected by this horrific act."

Orlando police said the event is unrelated to the murder of Christina Grimmie, the popular Voice singer who was killed while signing autographs after her Orlando show.